Method of coating hollow receptacles



Oct. 19, 1937. H. w. WEINHART 2,096,416

METHOD OF COATING HOLLOW RECEPTACLES Original Filed Dec; 27, 1953 INVEN 70/? By H. W. WE/NHART ATTORNEY Patented Oct. 19, 1937 PATENT OFFICE METHOD OF CQATIQ'G HOLLOW RECEP- LES Howard W. Weinhart, Elizabeth, N. J., assignor to, Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Original application December 27, 1933, Serial Divided and this application August 22, 1934, Serial No. 740,877

4 Claims. ,(CI. 91-68) This invention relates to a method of coating hollow receptacles and more particularly to a method of coating the interior wall of an electron discharge device, such as the cathode ray oscillograph device disclosed in my application Serial No. 704,101, filed December 27, 1933, of which application this is a division.

In-cathode ray oscillograph devices, it has been found that portions of the enclosing vessel 1 in the vicinity of the electron beam become electrically charged and thereby deleteriously affect the beam. In order to prevent this, it has been proposed to coat the inner walls of these portions of the enclosing vessel with a conductive material which may have. a suitable potential applied thereto to provide a field for focussing the electron beam projected toward a fluorescent screen at one end of the enclosing vessel. If such coatings are of metal they have the undesirable characteristic of reflecting light thereby impairing the intensity of the image produced upon the.

fluorescent screen. Furthermore, metallic coatings are .relatively expensive and often ,difiicult to, form. One object of this invention is-to form a continuous non-metallic coating onthe inner wall of ahollow receptacle, such as the' enclosing vessel of ,an electron discharge device.

Another object of this invention is to expedite the formation and to reduce the cost of forming such a coating.

In accordance with this invention, the enclosing vessel is provided with a removable inlet and a removable outlet, the inlet being connected to a reservoir containing colloidal graphite, known as Aquadag. The colloidal graphite is forced into the vessel by air under pressure and caused to rise to a desired level. The air trappedabove the incoming liquid is removed through the outlet pipe and when the desired amount of coating material has been introduced into the vessel, the air pressure in the reservoir is removed and applied to theoutlet. This back pressure forces the coating liquid into the reservoir thereby leaving a uniform deposit of colloidal graphite adhering to the inner wall of the vessel. The deposit is dried and then baked to form a hard and adherent coating.

This method facilitates-the formation of the coating and insures a uniform layer of material on all portions of the wall desired. Furthermore, the boundary of the coating "is readily controllable so that the coating does not mask another coating, such as a fluorescent screen, on a different 65 Portion of the vessel.

The invention and the features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in. which:

1 illustrates one embodiment of the appa- 5 ratus employed in producing a coating on the interior wall of a cathode ray discharge vessel, in accordance with this invention; and

. Fig. 2 is a. view in cross-section of an enclosing vessel for a cathode ray electron discharge de- 10 vice, coated in accordance with this invention.

Referring now to the drawing, the enclosing vessel comprises an elongated cylindrical portion or neck Ill and a flaring portion ll, terminating in a dome portion l2, which may be provided 15 with an internal highly eflicient fluorescent coating or screen l3 as disclosed in Patent 1,603,284, granted October 19, 1926 to John B. Johnson.- The coating or screen l3 becomes fluorescent upon impact of an electron beam which may be produced as described in the copending application mentioned above.

In order to prevent the building-up of electrical charges on the inner walls of the portions in and II, these walls are provided with a. non-metallic coating H of colloidal graphite, commercially known as Aquadag. .This coating, as clearly shown in Fig. 2, extends up to adjacent thev boundary of the fluorescent screen l3 and may have a suuitable potential applied thereto 30 through a. leading-in conductor l5, sealed in the wall of the cylindrical portion Hi.

In forming the coating M in accordance with this invention, the neck portion ll) of the vessel is provided with a removable plug l6 having an 35 inlet tube or connection I! which extends into the vessel a slight distance beyond the inner surface of the plug it. An elongated outlet tube l8 extends through the plug 16 and terminates within the vessel at a point slightly beyond the line 40 to which the coating is desired. The inlet connection I 'l to the discharge vessel is an elongated U-shaped tube which is connected to a reservoir l9 containing the coating liquid, such as colloidal graphite 20. A valve 2| for the reservoir is pro- 45 vided between the reservoir and the tube II. A similar valve 22 is inserted in the mouth of the reservoir and normally is in a closed condition except when it is desired to replenish the colloidal graphite material 20 within the reservoir. 50 Adjacent the valve 22 and above the level of the colloidal graphite coating material 20 is a tubular extension 23 to which may be connected any source of pressure such as an air pump, not shown.

v method of coating the inner wall of the vessel comprises opening the valve 2| and applying air pressure through thetube 23 to inject air into the reservoir I8, whereby the coatins material 20 is forced intothe vessel through the inlet connection l|. The pressure of air is maintained constant until the level of the coating liquid reaches the level indicated by the dotted line 24 in Fig. 1. During the filling of the vessel with the colloidal material all of the imprisoned air in the vessel, displaced by the liquid, is ejected through the outlet pipe l8 and when the level of the coating material reaches the line 24 the air pressure is removed from the connection 23 and applied to the open end 25 of the outlet pipe It. The pressure of air emerging from the inner end of the pipe l8 forces the liquid in the vessel back through the U-shaped connection i1 into the reservoir l9 and, when all the liquid is removed, the plug it, and pipe connections attached thereto may be taken out of the end of the portion Iii. After the coating operation iscompleted the vessel I is dried in an oven and baked to form a hard and adherent coating on theinner wall of the vessel.

This method enables and expedites the formation of a uniform coating on the wall of the vessel and effects a uniform boundary between the graphite coating and the fluorescent screen. Furthermore, due to the black, opaque coating on the wall of the vessel no reflections altering the indication of the electrical phenomenon exhibited on the fluorescent screen are present. Another advantage is the avoidance of a difference of expansion between the glass vessel and the coating, su'ch'as might be present if a metallic coating were applied to the inner wall of the vessel.

Although specific apparatus has been shown for producing a coating in accordance with. this invention, it will be understood, of course, that modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

l. The method of forming a coating on the inner wall of a vessel closed at one end and having an opening at the other end, which oomprises closing said opening with a stopper having an inlet connection, coupling said inlet connection to a reservoir containing a coating liquid, raising the pressure of the liquid in said reservoir with res ectto said vessel whereby said liquid flows into said vessel to a level adjacent said closed end of said vessel, and raising the pressure or the liquid in said vessel with respect to said reservoir whereby said liquid returns to .said reservoir.

2. The method of forming a coating on the inner wall of a vessel which comprises inserting inlet and outlet connections into said vessel, connecting the inlet to a reservoir containing a coating liquid, flowing the liquid into said vessel, elevating the liquid in said vessel by pressure to a'level intermediate the ends of said vessel, and impressing a back pressure on said liquid in said vessel through said outlet to return the liquid to said reservoir.

3. The method of forming a coating on the inner wall of a vessel which comprises inserting inlet and outlet connections into said vessel, connecting said inlet connection to a reservoir containing a coating liquid, flowing the liquid into said vessel, elevating the liquid in said vessel under pressure to a level intermediate theends of said vessel, impressing a back pressure on said liquid in said vessel through said outlet connection to return said liquid to said reservoir, drying the residue on the inner wall of said vesseL'and baking said vessel to form an adherent coating on said wall.

4. The method of forming a graphite coating on a restricted portion of the inner wall of a vessel below a boundary between the ends of said vessel, which comprises inserting an inlet pipe through one end of said vessel with its inner end below said boundary, inserting an outlet pipe through said one end until its inner end is substantially level with said boundary, connectinl said inlet pipe to a reservoir containing colloidal- 

